In ancient civilizations, the study of the planets and stars was carried out for two very practical purposes: time-telling and astrology. The opening chapter of Genesis, cited in our first blog entry, refers to the sun, moon and stars as the rulers of day and night: using the stars to make one’s calendar is completely right and proper. But the Bible’s attitude toward astrology is very different.

The Hebrews had a complex luni-solar calendar, based on the motions of the moon and the sun through the zodiac constellations. Holy days were related to the phases of the moon (which determined the length of the month) and the seasons of the sun. For example, Passover (from which we derive our Christian Easter) occurs on the first full moon in spring. The beginning of the solar year, whose seasons determine the planting and harvesting of crops, was determined by the high priests; they had the responsibility to add an extra month every two or three years, as they saw necessary, to keep the lunar calendar and the seasonal (solar) calendar more or less in sync.

By relying on the judgment of the priests, the ancient Hebrews avoided the need for a sophisticated mathematical model of how the sun and moon moved in the sky. The Greeks did work out such a system, however, which eventually became the basis of both the modern Jewish calendar (after the destruction of the temple in Jerusalem) and it was used for the Christian calendar, established at the council of Nicea in 325 and reformed by Pope Gregory XIII in 1582 — the occasion of the church hiring its first official astronomers, the forerunners of the modern Vatican Observatory.

The motions of the sun and moon are complicated, and it took a pretty sophisticated mathematics to work them out. But worked out they are; as we noted in our second blog, their regularity was one of the reassuring things about the universe to the writers of the Psalms, a sign of God’s constancy.

The motion of small bodies in the solar system is still a subject of intense research. Observing the colors and spin of the comet/asteroid Pholus, Steve Tegler (Northern Arizona University) and Brother Guy Consolmagno took this image with the Vatican’s telescope on Mount Graham, Ariz., as the object passed in front of the galaxy NGC 5964. We took three separate images in red, green and blue, and then combined them to make this image; since Pholus was moving between images, it appears as a rainbow

The motions of the planets, however, are far more complicated. The ancient Greeks tried to model them mathematically, but without complete success. The Roman astronomer Ptolemy came up with a system that he claimed fit his data, and it supported Aristotle’s idea of how the universe worked; but he may have fudged a few observations to make his theory work. (If so, he was not the first, or last, scientist tempted to shade the numbers to fit the model!) Copernicus and Kepler came up with better models in the early Renaissance, encountering furious opposition in the process, and even their methods were not perfect.

How tough is it to work out the positions of the planets? Consider this: just this month, October 2008, the Division for Planetary Sciences of the American Astronomical Society gave a major award to Jon Giorgini, a scientist at the NASA Jet Propulsion Laboratory in Pasadena, Calif., for deriving the current most widely used model of the motions of the planets and asteroids. It is still a current topic of research, especially in an age when we send spacecraft to land on planets, or point their cameras at tiny asteroids, and we need to know their positions to very high accuracies.

Nowadays we need those positions for our spacecraft; but why did ancient peoples put so much effort into predicting the positions of the planets? The planets don’t control the growth of crops, like the sun does, or the tides like the moon; there was no practical application for this knowledge back then — except for this: to use the motions of the planets to cast horoscopes.

The logic behind astrology is understandable, if flawed. Events in our human lives seem to repeat, good times and bad, good crops and bad, victories and defeats in wars; and so it was tempting to try to predict from the rhythm of past events what is going to happen next. (Stockbrokers continue to try to do that even today — with a questionable level of success, as seen in the current economy.) If the sun and moon can control things like crops and tides, could it be that the complicated rhythm of planetary positions might be responsible for other human activities?

After 3,000 years of astrological predictions, it is pretty obvious to most astronomers that astrology just doesn’t work. (If it did work, then why is it that astrologers and fortune tellers are found only in the poorest districts of town?) But that wasn’t at all obvious 3,000 years ago. Instead, the wisest men of almost every civilization spent an enormous effort to try to keep track of planetary positions, to try to correlate them with human events.

Almost every civilization did this — but not the ancient Hebrews. It wasn’t for lack of faith in the stars, but for a far more interesting reason. Here is what the books of Wisdom has to say about using the stars to predict the future:

Wis 13:1-5 For all people who were ignorant of God were foolish by nature; and they were unable from the good things that are seen to know the one who exists, nor did they recognize the artisan while paying heed to his works; but they supposed that either fire or wind or swift air, or the circle of the stars, or turbulent water, or the luminaries of heaven were the gods that rule the world. If through delight in the beauty of these things people assumed them to be gods, let them know how much better than these is their Lord, for the author of beauty created them. And if people were amazed at their power and working, let them perceive from them how much more powerful is the one who formed them. For from the greatness and beauty of created things comes a corresponding perception of their Creator.

The idea that the stars are some sort of gods who control human events is specifically condemned by the Bible. For one thing, it is a kind of paganism. The book of the law, Deuteronomy, is quite specific about this:

Dt 4:19 And when you look up to the heavens and see the sun, the moon, and the stars, all the host of heaven, do not be led astray and bow down to them and serve them, things that the LORD your God has allotted to all the peoples everywhere under heaven.

We are not subject to the stars; rather, we are to use them, not let them use us.

This condemnation is repeated elsewhere in the Old Testament. Perhaps the most interesting development on this front, however, is found in Isaiah. Notice here that the reasons against astrology and fortune-telling now go beyond merely the admonition against worshipping other gods.

Is 47:10-14 You felt secure in your wickedness; you said, “No one sees me.” Your wisdom and your knowledge led you astray, and you said in your heart, I am, and there is no one besides me.” But evil shall come upon you, which you cannot charm away; disaster shall fall upon you, which you will not be able to ward off; and ruin shall come on you suddenly, of which you know nothing. Stand fast in your enchantments and your many sorceries, with which you have labored from your youth; perhaps you may be able to succeed, perhaps you may inspire terror. You are wearied with your many consultations; let those who study the heavens stand up and save you, those who gaze at the stars, and at each new moon predict what shall befall you. See, they are like stubble, the fire consumes them; they cannot deliver themselves from the power of the flame. No coal for warming oneself is this, no fire to sit before!

It is not enough merely that astrology doesn’t work; it would be immoral even if it did work. The consuming fire that Isaiah refers to is not the result of being led astray by these sorceries — “perhaps you may be able to succeed,” he notes. Rather, it is the moral destruction that comes to anyone who tries to use the arts of the world to control the freedom of other people. Ultimately, the crime of the astrologer is the denial of free will. If one believes that human actions are controlled by the stars, one denies both the power of God and the power of the free soul made in the image and likeness of God.

There is one interesting result of this biblical condemnation of astrology. When, many hundred years after Moses and Solomon and Isaiah, a group of astrologers from the East showed up in Jerusalem with charts and diagrams, Herod and the high priests were completely taken by surprise. They didn’t know their astrology. They were unaware of the configuration of the planets and their purported meaning. They had to wait for the Magi to tell them of a newborn King.